I think the main difference between the 305's and the 405's is that the 305 is a longer grip which allows/needs less of a "grip filler". The shorter 405's need the fatter/fuller stock to wrap your fingers around. (That make any sense?)
I carried a (non-airweight) model 36 for years. Wasn't rated for +P, but did fire a few stout handloads. Never thought much about the recoil.
A couple of years ago my DW gave me an airweight 638 for Christmas. It was basically the same as my 36 without a rust or pocket snagging problem and I could still fire SA if desired. But right from the first I found it unpleasant to fire. I shoot enough to stay proficient, but no more and I can't say I enjoy it.
Not the same kind of boom and muzzle flip of a magnum, more like having the palm of the hand slapped with a ruler kind of unpleasant - different from the 36.
I added the LG405 laser grips, not expecting it to reduce the sting (although I'm sure it helps), but because I found the 638 much less accurate than my 36. May have been the sights are off, or my old(er) eyes, flinching, or just the damn short sight radius, but they make a huge difference in accuracy.
And the bottom line is I chose the 405's over the 305's because they are more concealable. If the recoil is really objectionable, I'd suggest some mild target loads for proficiency at the range. Save the +P's for the real thing when recoil will be the last thing on your mind.